Omit Sender verify for certain mails?

Hi
This should sound extrange, but we have a client who needs to receive emails from a couple of addresses that doesn't pass sender verification.
We alredy tryed to talk to the other end to correct the problem, but there are huge Companies and wont' change their policy ..... so here we are......
We have sender verification activated (and want to keep it htat way), so want to know if its possible to bypass sender verification for some addresses. Don't know witch is better, a whole domain, IP address, individual email address, but at this point, any option may help.
Thanks

Thank you for you reply,
Could you be so kind and be a little more spcecific on where should I put the
!senders = +whitelist_senders

Here is our config

#!!# ACL that is used after the RCPT command
check_recipient:
# Exim 3 had no checking on -bs messages, so for compatibility
# we accept if the source is local SMTP (i.e. not over TCP/IP).
# We do this by testing for an empty sending host field.
accept hosts = :

accept hosts = +auth_relay_hosts
endpass
message = $sender_fullhost is currently not permitted to \
relay through this server. Perhaps you \
have not logged into the pop/imap server in the \
last 30 minutes or do not have SMTP Authentication turned on in your email client.
authenticated = *

deny message = $sender_fullhost is currently not permitted to \
relay through this server. Perhaps you \
have not logged into the pop/imap server in the \
last 30 minutes or do not have SMTP Authentication turned on in your email client.

#!!# ACL that is used after the DATA command
check_message:
require verify = header_sender
accept

#!!# ACL that is used after the RCPT command
check_recipient:
# Exim 3 had no checking on -bs messages, so for compatibility
# we accept if the source is local SMTP (i.e. not over TCP/IP).
# We do this by testing for an empty sending host field.
accept hosts = :

accept hosts = +auth_relay_hosts
endpass
message = $sender_fullhost is currently not permitted to \
relay through this server. Perhaps you \
have not logged into the pop/imap server in the \
last 30 minutes or do not have SMTP Authentication turned on in your email client.
authenticated = *

deny message = $sender_fullhost is currently not permitted to \
relay through this server. Perhaps you \
have not logged into the pop/imap server in the \
last 30 minutes or do not have SMTP Authentication turned on in your email client.

#!!# ACL that is used after the DATA command
check_message:
# Enabling this will make the server non-rfc compliant
# require verify = header_sender
accept

I have customized my configuration to use different lists for various things in my ACLs. The first section is where the lists are put and other types of customisations. You;d need to look at the exim docs to see what else can be customised there. Other sections of exim.conf (the ACLs) refer to the first section when I reference a list. You reference a list as +listname - example if I wanted to use /etc/exim/sender_whitelist I'd refer to it in an ACL as +sender_whitelist. If you haven't used any lists or customised anything else, it's not uncommon to have a blank first section.